The present invention relates generally to electronic energy meters, and more particularly to highly functional programmable electronic energy meters with systems for service identification and power quality analysis.
Programmable electronic energy meters are rapidly replacing electromechanical meters due to the enhanced functionality achieved using programmable logic integrated into solid-state electronic meters. Some of these meters can be used to meter various different electrical services without hardware modification. For example, meters having a voltage operating range between 98 Vrms to 526 Vrms are capable of operation with either 120 V or 480 V services. U.S. Pat. No. 5,457,621, dated Oct. 10, 1995, entitled SWITCHING POWER SUPPLY HAVING VOLTAGE BLOCKING CLAMP, assigned to ABB Power TandD Company discloses examples of such meters. In addition, some meters are constructed for use with any 3-wire or any 4-wire service, also disclosed in U.S. Pat. No. 5,457,621. Unless meters having this versatility are used, utilities must be careful to install the correct meter in relation to both configuration and electrical service supplied at the installation site. Unfortunately, meter installers are not always trained to detect or note service particularities which might indicate that the meter to be installed is not configured properly for a particular installation.
For this reason, some utilities configure the meters themselves to ensure better control over which meters are installed at which installation sites. However, such configuration activity adds to the installation cost and does not always reduce the risk that a meter configured for one service might inadvertently be installed at a site supplied by a different service. Therefore, there remains a need for an electronic meter which automatically detects the service type and voltage to which the meter is installed and which either automatically configures its own programming to the detected service or provides a simple means for manual configuration at the installation site.
Further, the performance of power quality tests requires that the type of service and service voltage be known prior to installation so that the meter""s programming can be locked to the appropriate service-dependent thresholds utilized in connection with particularized power quality tests. Therefore, for this additional reason, there remains a need for an electronic meter to automatically detect the service type and voltage to which the meter is installed and which automatically configures its programming to the detected service.
In addition, many new electronic energy meters have begun to take advantage of their programming capabilities by providing limited diagnostic and/or power quality testing. These capabilities are provided by programming stored in read only memory (ROM). Thus, these meters are currently limited in operation to predefined programming, such as predefined sets of tests. Significantly, such meters are also limited to the measurement of only a predetermined set of parameters that have been programmed into such meters, i.e., stored in ROM, during manufacture. Consequently, any change to the measurements or tests supported by the meter must be carried out by replacing the meter""s ROM, i.e., by factory modification. Therefore, there also exists a need for a more flexible electronic energy meter that permits the addition of new measurements or testing capabilities without requiring factory modifications to effect such functionality changes.
The meter includes firmware which measures the characteristics of electrical energy supplied to the meter and which generates characteristic signals reflective of the measured characteristics of the electrical energy. A processor is connected to receive and process the characteristic signals. The processing of the characteristic signals includes selecting and manipulating certain of the characteristic signals and generating characteristic information in response to the selection and generating additional characteristic information in response to the manipulation. It is preferred for the meter to include a memory having reference information stored therein. In such an embodiment, the manipulation of characteristic signals includes retrieving certain of the reference information and generating the characteristic information in response to the selected signals and the reference information.
The present invention is directed to a system for monitoring power quality events of electrical energy provided to an energy meter via a service type, comprising: storage means for storing reference information reflective of different service types; means for measuring characteristics of the electrical energy; and means for retrieving the reference information from the storage means and comparing the measured characteristics to the reference information for the service type to determine the occurrence of power quality events.
In accordance with an aspect of the present invention, the system further comprises memory means for recording at least one of a start time, a duration, a stop time, a measured phase, a magnitude of a measured quantity, and a predisturbance value for each of the power quality events, and a cumulative total of the power quality events. Preferably, the storage means and the memory means comprise an EEPROM.
According to further aspects of the invention, the means for measuring comprises a digital signal processor and the means for retrieving and comparing comprises a microcontroller.
In accordance with an aspect of the present invention, the system further comprises an alarm and means for activating the alarm responsive to the occurrence of the power quality events.
In accordance with an aspect of the present invention, the system further comprises display means for indicating the occurrence of the power quality events and/or for displaying a number of occurrences of the power quality events.
In accordance with a further aspect of the present invention, the power quality events comprise at least one of abnormal service, low voltage, high voltage, reverse power, abnormal service current, low current, abnormal power factor, excess second harmonic current, excess total harmonic distortion in the current, excess total harmonic distortion in the voltage, flicker, and momentary voltage sag. The power quality events to be monitored are selectable and the power quality events comprise algorithms that are programmable.
Preferably, the power quality events are monitored using predetermined thresholds that are tunable. The thresholds comprise at least one of time, voltage, current, power factor, and percentage. The thresholds are responsive to the service type which provides electrical energy to the energy meter.
In accordance with a further aspect of the present invention, the service type is single phase or multiphase, and the power quality events are checked for each phase when the service type is multiphase. The power quality events are checked for a combination of phases when the service is multiphase.
In accordance with a further aspect of the present invention, the means for measuring characteristics of the electrical energy measures the characteristics over a predetermined and tunable time period.
In accordance with a further aspect of the present invention, the means for comparing the measured characteristics comprises programmable comparison routines.
In accordance with further aspects of the present invention, the reference information comprises a plurality of power factor limits stored in a power factor test limit table. When the service type is multiphase, the power factor limits in the power factor test limit table are accessed in a first direction when the service type has an ABC rotation, and the power factor limits in the power factor test limit table are accessed in a second direction when the service type has a CBA rotation. Preferably, the second direction is opposite the first direction.
Another embodiment within the scope of this invention includes an electronic processor-implemented process for monitoring power quality events in electrical energy provided to an energy meter via a service type, comprising the steps of: storing reference information in a memory reflective of different service types; measuring characteristics of the electrical energy provided to the energy meter; and retrieving the reference information from the memory and comparing the measured characteristics to the reference information for the service type to determine the occurrence of power quality events.
In accordance with a further aspect of the present invention, the process further comprises the step of recording in a second memory at least one of a start time, a duration, a stop time, a measured phase, a magnitude of a measured quantity, and a predisturbance value for each of the power quality events, and a cumulative total of the power quality events.
In accordance with a further aspect of the present invention, the process further comprises the step of checking power quality events for a combination of phases when the service type is multiphase.
According to further aspects of the invention, the step of comparing the measured characteristics comprises comparing the reference information and the measured characteristics using programmable comparison routines.